This invention relates to hydraulic control means for an auxiliary shield positioned at the side of a protective shield of a mine roof support unit.
It is known to provide a mine roof support unit with an auxiliary shield which can be moved laterally thereof to seal the gap between that unit and the adjacent unit. Such an auxiliary shield is usually positioned at the side of the roof shield, but it could also be positioned at the side of the goaf shield of the roof support unit. Such an auxiliary shield is moved either by springs or by hydraulic rams. Such auxiliary shields can also be used to assist the process of guiding and aligning the roof support units when they are advanced to follow up the advance of the face being won (see DE-OS No. 2 032 208 and DE-AS No. 2 210 757).
DE-AS No. 2 350 482 discloses hydraulic control means for such an auxiliary shield, the hydraulic control means being constituted by pilot-controlled two-way valves and manually-operated control valves. The arrangement is such that the rams associated with the auxiliary shield are automatically connected to a high pressure line when the props of the adjacent roof support unit are relieved of load, and are automatically connected to a return line when those props are pressurised. In order that such a roof support unit can be aligned, the rams associated with the auxiliary shield manually-operable control valve device, it is possible to guide and align an unloaded roof support unit even when its auxiliary shield is "hydraulically locked".
Advantageously, the control valve device is constituted by two control valves for each hydraulic ram, one control valve controlling extension of its respective hydraulic ram and the other control valve controlling retraction of that ram. Preferably, the or each pilot check valve is positioned in a line leading from said one control valve associated with a given hydraulic ram to that hydraulic ram.
The invention also provides a mine roof support unit comprising a roof shield supported by hydraulic props, an auxiliary shield positioned at one side of the roof shield, at least one hydraulic ram for moving the auxiliary shield laterally of the roof shield, and hydraulic control means for controlling the movement of the auxiliary shield, wherein the hydraulic control means is as defined above.
Preferably, the or each hydraulic ram is double-acting.
Advantageously, there are three hydraulic rams and two pilot check valves, one hydraulic ram being associated with one pilot check valve and two control valves, and the other two hydraulic rams being associated with the other pilot check valve and two control valves. With this arrangement, not only can the auxiliary shield be moved out have to be double-piston rams, the pressurisation of one piston of which is controlled by way of the pilot-controlled two-way valves, the pressurisation of the other piston being effected by way of the manually-operated valves. One disadvantage of this arrangment is that double-piston rams are required. Another disadvantage is that control of the auxiliary shield of one roof support unit proceeds in dependence upon the pressurisation of the props of the adjacent roof support unit. Moreover, the rams associated with each auxiliary shield can only be actuated together, so that only limited alignment of the roof support units is possible.
The aim of the invention is to provide hydraulic control means for the auxiliary shield of a mine roof support unit, which control means does not suffer from these disadvantages.